1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a back light unit used as a light source in a liquid crystal display (LCD), as well as a method for assembling the back light unit.
2. Discussion of the Related Art
A back light unit of a conventional LCD is comprised of a reflecting sheet, a light guide, a diffusing sheet, a lamp and a lamp housing. This back light unit is described below with reference to FIGS. 1 and 2. FIG. 1 is a three-dimensional view showing a back light unit of a conventional LCD. FIG. 2 is a cross-sectional view taken along line II-II' of FIG. 1.
This conventional back light unit includes a reflecting sheet 103, a light guide 104, a diffusing sheet 105, a lamp 102, a U-shaped lamp housing 140 and a frame 110 for fixing these elements. The reflecting sheet 103 is attached to the lower surface of the light guide 104 and the diffusing sheet 105 is attached to the upper surface of the light guide 104. The lamp 102 is placed in the U-shaped lamp housing 140 and fastened to one side of the light guide 104. The U-shaped lamp housing 140 (alternatively referred to as a "reflector") encompasses the lamp 102 and partially encloses one edge of the light guide 104. The lamp housing 140 also reflects light from the lamp 102 to the light guide 104, resulting in most of the light from the lamp 102 being directed to the light guide 104. As described above, the lamp 102 is positioned in a space made by the lamp housing 140 and the light guide 104. The light guide 104 has a diffusing sheet 105 on its upper surface. Each edge of the diffusing sheet 105 may have adhesive materials in order to prevent its detachment from the light guide 104. Reference numeral 109 in FIG. 2 points to a wire coming from the lamp 102. The back light unit which includes the reflecting sheet 103, the light guide 104, the lamp 102 and the lamp housing 140 is fixed by a frame 110 which is formed, for example, by an injection molding of plastics. A liquid crystal display panel 120 includes two substrates which are opposite to each other and have planarization plates on their outer surfaces. This liquid crystal display panel 120 is positioned on the back light unit.
The lamp housing 140 of the back light unit fastens the lamp 102 to one side of the light guide 104 and reflects light transmitted from the lamp 102. As shown in FIG. 2, the lamp housing 140 is made, for example, of hard metal or plastics and partially encloses one edge of the light guide 104. The lamp housing 140 includes a light reflecting element which directs light transmitted from the lamp 102 to the light guide 104.
The procedure for fastening the lamp, the lamp housing and the light guide will now be described with reference to FIG. 3. The lamp 102 is placed in the space within the U-shaped lamp housing 140. If the diameter of the lamp 102 is smaller than this space within the U-shaped lamp housing, then an assistant fastening element encompassing the lamp 102 is provided to prevent motion and provide a stabilizing support of the lamp within the space. One edge of the light guide 104 is enclosed by the lamp housing 140, thereby the lamp 102 is fastened. The lamp housing 140 is placed on the edge of the frame 110. The height of one edge of the light guide 104 enclosed by the lamp housing 140 is preferably the same as the diameter of the lamp 102 to provide a stable fastening. The space made by the U-shaped lamp housing 140 has the same height as the edge of the light guide 104 that is enclosed by the lamp housing. As a result, the light guide 104 can not be put into the lamp housing 140 smoothly, which makes the fastening together of the light guide 104 and the lamp housing 140 time consuming and difficult. When manufacturing a conventional LCD, the step of fastening the lamp housing 140 to the light guide 104 results in an increase in manufacturing time and often results in damaged products.
Further, the frame 110 which fixes the back light unit and the liquid crystal display panel 120 is easily twisted and bent when using the LCD for many hours because the frame 110 of this conventional arrangement is made by the injection molding of plastics. In addition, because of the injection molding procedure used to manufacture this frame 110, it has a predetermined limited width and can not be formed thinner than this limited width. As a result, it is impossible to manufacture a thinner LCD.